The pituitary gland is the pivotal endocrine organ. Pituitary tumors occur in ~20% of the population and comprise 10% of all brain tumors. Functional pituitary tumors result in life-threatening diseases, infertility and impotence. Clinically non-functional (NF) tumors cause hypopituitarism or blindness and there is no available medical treatment or specific imaging technique for these tumors. The PI's long-term goal is to determine the molecular factors controlling their proliferation, and to exploit these insights to develop novel therapy and imaging. The focus of this proposal is the folate receptor (FRa) in NF tumors, because a) NF tumors are the most common pituitary tumors, b) we discovered that FRa mRNA is uniquely overexpressed in NF tumors, c) the FRa holds significant promise for medical treatment for NF tumors by enabling molecular imaging and targeting of NF tumors to identify and select tumors that may respond to folate targeted therapy, and d) the PI has a large bank of human pituitary adenomas for the studies needed to execute this proposal. Our hypotheses are that, i) FRa overexpression enhances tumor proliferation, ii) FRa receptor targeting with folate coupled cytotoxic agents can inhibit tumor proliferation, iii) a FRa targeted imaging agent can identify FRa - expressing pituitary tumors by radionuclide imaging in vivo. The non-invasive diagnosis of tumor receptor expression to allow selection of NF tumors that may be treatable by targeted therapy opens up novel opportunities. Similar discoveries and applications of receptor biology led to new drugs for the treatment of prolactin-secreting tumors (bromocriptine, carbegoline) and growth-hormone secreting tumors (somatostatin, pegvisomant) with less need for surgery. In Aim 1, we will test the hypothesis (i) by cell culture of a pituitary tumor cell line, aT3-1, which is a model of human NF tumors. An expression vector containing the FRa cDNA or a dominant negative mutant FRa cDNA will be transfected into aT3-1 cells. Cell proliferation will be measured by cell counts, BrdUrd-PI, and proliferating cell antigen flow cytometry. The transforming property of FRa will be evaluated in soft agar. Tumorigenicity will be assayed by inoculating FRa transfected cells into nude mice and measuring tumor growth. In Aim 2, we will test the hypothesis (ii) by culturing human pituitary tumor cells with folate-PEG-liposomes carrying the antineoplastic drug doxorubicin. We will determine the cytotoxicity efficacy of doxorubicin on human tumor cells in vitro by the MTT cytotoxicity assay. In Aim 3, we will test the hypothesis (iii) by using a FRa targeted technetium-99 labeled radionuclide imaging molecule to identify FRa - expressing pituitary tumors in human subjects (in vivo). These experiments capitalize on our findings of selective overexpression of functional FRa in NF adenomas, thereby translating basic research into clinical application.